A study of geological age of the Mesozoic volcanic-sedimentary strata in Xiehe' rside area, Horqin Right Wing Middle Banner, Inner Mongolia

A suite of Mesozoic strata is exposed in the Xiehe' rside area of Horqin Right Wing Middle Banner, Inner Mongolia. The lithological association is mainly composed of acidic pyroclastic rock and pyroclastic sedimentary rock intercalated with clastic sedimentary rock and acidic volcanic lava. Based on the fossil woods discovered in the upper layer of the strata by 1:50000 regional survey, the authors hold that the formation time is middle-late Jurassic. Combined with the lithological association, the authors assigned the strata to the Upper Jurassic Manketouebo Formation. In order to accurately redefine the stratigraphic age and provide a basis for the study of the age of fossil woods and the regional biostratigraphic.correlation, the authors collected zircon testing samples from the acidic pyroclastic rock in the horizon lower than that of the fossil woods, and determined that the zircon U-Pb age is (165±1) Ma, belonging to middle Jurassic. In addition, the age of the porphyritic fine-crystalline grained diorite which invaded the strata was obtained, and the zircon U-Pb age is (131±1) Ma, which defines the upper age limit of the strata. According to the regional correlation of lithological associations, dating results, time of fossil woods assemblage, and characteristics of attitude of strata, the authors conclude that the strata should be assigned to Middle Jurassic Xinmin Formation and constitute a part of the filler of Tuquan volcanic-sedimentary basin.